Method of making printed circuits



NOV 12, 1958 J. SMITH` JR., ETAL 3,410,743

METHOD OF MAKING PRINTED CIRCUITS Filed Sept. 28. 1964 l' 2y-f IN VEN TORS dmes SmzZLc/z'z, ZYZuzz cf acme, Wormen .Jaw/ff:

United States Patent O 3 410,743 METHOD F MAKING PRINTED CERCUITS James Smith, Jr., Melvin J. Racine, and Norman D. Lawless, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Sept. 28, 1964, Ser. No. 399,669 6 Claims. (Cl. 156-233) ABSTRACT OF THE DISCLOSURE A method of making printed curcuits including the steps of cutting the desired conductor path pattern from a metal* lic foil and embedding the pattern in one surface of a sheet of paper while forming supporting ridges in the opposite surface of the paper to facilitate the transfer and subsequent application of the pattern to an insulator.

This invention relates to an improved method of making printed circuits.

Printed circuits have become Well known in the art and usually include a conductive pattern of desired circuit conguration which may be bonded or otherwise secured to an insulating base and used to interconnect electrical components.

Because of the desirable characteristics of printed circuits, various manufacturing techniques have been utilized in an leffort to decrease the production costs thereof and to increase the speed of production and the quality of the article produced.

None of the prior art methods of making printed circuits have been entirely satisfactory. For example, in the so called dinking die process, the electrically conductive material is subjected to stress and distortion during the cutting operation and where the material is placed on the insulating base prior to cutting there is a risk of weakening the base material. In addition the die requires a delicate knife edge necessitating frequent sharpening which is a difficult and expensive operation.

In accordance with the present invention, an improved method of making printed circuits is provided in which a conductor path pattern is cut from a conductive foil and embedded in a fibrous material and thereafter pressed out of the fibrous material onto an insulating base. More particularly, a sheet of conductive foil and a sheet of paper are subjected to a die stamping operation wherein the conductor path pattern is cut from the foil and embedded in the paper without stressing or distorting the foil. Supporting ridges are formed in the paper during the stamping operation to vfacilitate transfer of the foil and paper to additional apparatus adapted to press the conductive pattern out of the paper and onto an insulating base.

A more complete understanding of the present invention may be had from the following detailed description which should be read in conjunction with the drawings in which:

FIGURES l and 2 are enlarged cross sectional views of a portion of a punch press adapted to form the desired conductor path pattern and illustrate stages in the manufacture of the printed circuit;

FIGURE 3 and 4 are cross sectional views of heated platens and illustrate other stages in the manufacture of the printed circuit;

FIGURE 5 is an elevational view of a portion of the printed circuit with the paper transfer material being stripped away.

Referring now to the drawings and initially to FIG- URE 1, there is shown an enlarged portion of a die which may be mounted on the movable member of a conventional punch press and a support member 12 which may be secured to the stationary portion of the punch press. The die 10 is adapted to cooperate with the member 12 and a sheet of paper or other fibrous material 14 to cut the desired conductor path pattern from a blank sheet of copper or other conductive foil 16 and to embed the pattern into the paper.

The desired pattern may be engraved or otherwise formed on the die 10. Only a portion of the pattern is shown in FIGURE 1 as indicated by the embossed por tion 18. It will be noted that the cutting edge of the portion 18 has about a 15 draft angle but is substantially square rather than the delicate knife edge used in the dinking die process. A pair of round pressure bars 20 which may be made of soft steel Wire or hard rubber rods reside in grooves 22 formed on each side of the embossed portion 18. Placing the pressure bars 20 next to all of the cutting edges aids in the cutting action of the die 10.

The support member 12 is provided with grooves which follow the desired pattern configuration and are located in the support member beneath the embossed portion 18 of the die 10. One such groove is shown at 24. The groove 24 provides a relief for the paper during the stamping operation and is approximately .01 inch smaller on each side than the embossed portion 18 and has a 45 draft angle whereby the paper is released freely. Additional grooves such as indicated at 26 are also provided in the surface of the support member 12 for purposes which will become apparent hereinafter.

Referring now to FIGURE 2, it will be apparent that as the die 11i is lowered, the embossed portion 18 will initially contact the copper foil 16 and begin to embed the pattern into the paper 14. The pressure bars 20 then contact the portions 28 of the foil 16 to hold the foil in place during the cutting operation, insuring that both sides of the conductor path will be cut even though one side may be cut before the other. Further movement of the die 10 causes a conductor path 3i) to be cut from the remaining portions of the copper foil 16. The portion of the paper 14 which is directly below the pattern is forced into the groove 24 forming ridges 32, and tie bars 34 are formed in the paper 14 as it is pressed into the additional grooves The tie bars 34 give strength and support to the paper After the conductive path pattern has been embedded in the paper 14, the die 10 is raised and the skeleton or remaining portions of the conductive foil which do not form a part of the conductor path pattern are salvaged in a known manner. The paper 14 with the 4conductive pattern embedded therein is now placed in contact with an insulating base member 36 such as phenolic hard board having a heat-activated adhesive coating 38 on one surface thereof. The support 36 and the paper 14 are placed between heated platens 40 and 42. As the platens 40 and 42 are closed, the platen 42 engages the ridges 32 on the back of the paper 14 thereby pressing out the conductor path 30 intro engagement with the insulating base member 36 as shown in FIGURE 4. The paper 14 has been previously treated with a release agent such as silicon prior to the cutting operation and therefore is prevented from sticking to the adhesive coating 38 on the insulating base 36 so that the paper may be stripped away leaving the copper conductors adhered to the insulating base 36 as shown in FIGURE 5. Depending upon the use to be made of the printed circuit, an overlay insulation may be applied to the circuit at this time.

It will be apparent from the above that the paper 14 serves a dual purpose. The iirst use is in the actual cutting of the copper foil. The use of paper against the support member 12 tends to combine the cutting effects of a tted male and female die and a rubber pad die. The paper allows considerable mismatch and interference between the die 10 and the support member 12 without atectin g the cutting action. This allowable mismatch makes possible la suitable amount of tolerance in engraving the complex pattern in the die 10. The second function of the paper is to transport the conductor path pattern after it has been cut until it is transferred and adhered to the desired insulating base member 36.

The transfer and adhesion of the conductor path pattern to the insulating base member may also be accomplished by alternative methods. For example, the heatactivated adhesive may be .applied to the top surface of the foil 16 prior tothe die cutting operation rather than to the surface of the insulating base 36. Furthermore, a pressure sensitive adhesive may be used instead of the heatsensitive adhesive in which case non-heated platens are utilized. Moreover, transfer and adhesion may be accomplished with heated or non-heated rollers in the place of the platens 4f) and 42 in which case a flexible insulating base material such as Mylar is utilized.

While the preferred embodiment of the invention has been herein illustrated and described, it should be understood that the invention may be embodied in other forms within the scope of the following claims.

We claim:

1. A method of making printed circuits comprising cutting a desired conductor path pattern from a conductive metallic foil and embedding said pattern into one surface of a fibrous material, forming pattern ridges in the opposite surface of said fibrous material in accordance with said pattern, placing said one surface of said fibrous material in engagement with an insulating material, applying pressure to said insulating material and the pattern ridges of said fibrous material to transfer and secure said conductor pattern to said insulating material and removing said fibrous material from said insulating material.

2. A method of making printed circuits comprising cutting a desired conductor path pattern from a conductive metallic foil and embedding said pattern into one surface of a fibrous material, forming pattern ridges in the opposite surface of said fibrous material in accordance with said pattern, forming additional ridges in said opposite surface of said fibrous material to strengthen said fibrous material, placing said one surface of said fibrous material in engagement with an insulating material, applying pressure to said insulating material and said pattern ridges and ladditional ridges of said fibrous material to transfer and secure said conductor path pattern to said insulating material, and removing said fibrous material from said insulating material.

3. In a fabrication of printed circuits, a method of adhering a conductor path pattern to an insulating base material comprising cutting the desired conductor path pattern from a conductive metallic foil and embedding said pattern in one surface of a fibrous material, forming pattern ridges in the opposite surface of said fibrous material in Vaccordance with said pattern, placing said fibrous material in contact with an insulating base member, the contacting surface of the insulating base member having a heat-activated :adhesive coating thereon and the contacting surface of said fibrous material having a release agent thereon, applying pressure to said insulating base member and the pattern ridges of said fibrous material to transfer said pattern to said insulating base member, applying heat to said coating to insure adherence of said pattern to said insulating base member and removing said fibrous material.

4. The method of making a printed circuit where in a conductive pattern is formed and secured to at least one surface of an insulating base, said method comprising applying a conductive metallic foil to a sheet of paper, placing the foil and paper in a punch press having an upper die provided with the desired conductor path pattern embossed on the surface thereof, and a lower support member provided with grooves formed therein in the desired `conductor path pattern, closing said press to cut said pattern from said foil and embed said pattern into one side of said paper while pressing said paper into said groove to form ridges on the opposite side of said paper, placing said foil and paper in contact with said insulating base and applying pressure to said ridges to transfer and secure said pattern to said base and removing said sheet of paper.

5. A method of making printed circuits comprising cutting desired conductor path pattern from a conductive metallic foil and embedding said pattern into one surface of a fibrous material, forming pattern ridges in the opposite surface of said fibrous material in accordance with said pattern, forming additional ridges in said opposite surface of said fibrous material to strengthen said fibrous material, removing the remaining portion of the conductive foil not a part of the conductive pattern from the fibrous material, placing said one surface of said fibrous material lin eng-agement with an insulating material, applying pressure to said insulating material and said pattern ridges and additional ridges `of said fibrous material to transfer and secure said conductor path pattern to said insulating -material and removing said fibrous material from said insulating material.

6. A method -of making printed circuits comprising feeding a strip of copper foil and a contiguous strip of paper into a punch press having an upper die member provided with a desired conductor path pattern embossed thereon and having a lower support member provided with grooves formed therein which follow said conductor path pattern, cutting said desired pattern from said foil and embedding said desired pattern into one surface of said paper and forming pattern -ridges in the opposite surface of said paper, removing the remaining portions of the conductive foil not a part of the conductor pattern from the paper, placing said paper with said conductive pattern embedded therein in contact with an insulating material, the contacting surface of the paper having a release agent thereon and the contacting surface of the insulating material having :a heat-activated adhesive coating thereon, applying heat to said coating to insure adherence of said pattern to said insulating material and removing said paper from said insulating material.

References Cited UNITED STATES PATENTS 2,969,300 1/1961 Franz 156-233 DOUGLAS J. DRUMMOND, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,410 743 November l2 1968 James Smith, Jr. et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 52, beginning with "applying" cancel all to and including "material." in line 55, same column 4, and insert applying pressure to said insulating material and the pattern ridges of said paper to transfer said Conductive pattern to said insulating material.

Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

